1. Field of the Invention
The corrosion inhibiting system of the present invention is generally related to a method for inhibiting corrosion of a component of a marine vessel and, more particularly, to a method for inhibiting galvanic corrosion of a marine propulsion device of a marine vessel which automatically adapts to the presence or absence of a workable measuring electrode.
2. Description of the Prior Art
It is well known to those skilled in the art of marine vessels and marine propulsions systems that galvanic corrosion can be exacerbated by connecting the marine vessel to a shore power system without appropriate protection. Several types of cathodic protection devices are commercial available. One such type of device is available in commercial quantifies from the Mercury Marine division of the Brunswick Corporation and is referred as a mercathode system. As is also well known to those skilled in the art, faulty components in the electrical system of a marine vessel or its cathodic protection device can result in either galvanic corrosion or a dangerous condition.
U.S. Pat. No. 4,528,460, which issued to Staerzl on Jul. 9, 1985, discloses a cathodic protection controller. A control system for cathodically protecting an outboard drive unit from corrosion includes an anode and a reference electrode mounted on the drive unit. Current supplied to the anode is controlled by a transistor, which in turn is controlled by an amplifier. The amplifier is biased to maintain a relatively constant potential on the drive unit when operated in either fresh or salt water.
U.S. Pat. No. 6,265,879, which issued to Landreth on Jul. 24, 2001, describes an electrical integrity test system for boats. The system provides circuitry for evaluating the integrity of the boats galvanic isolator. The integrity test system includes two single reference diodes and a circuit for applying DC voltage across the reference diodes and the galvanic isolator. Another micro-controller stores the values of the voltage drops across the galvanic isolator and the voltage drops across each reference diode and subsequently determines if the voltage drop across the galvanic, isolator is that to be normally expected. If it is not, then the system informs the operator that the boat""s galvanic isolator is not operating properly.
U.S. Pat. No. 5,627,414, which issued to Brown et al on May 6, 1997, describes an automatic marine cathodic protection system using galvanic anodes. An automatic system uses sacrificial galvanic anodes to provide a controlled and optimum amount of cathodic protection against galvanic corrosion on submerged metal parts. Intermittently pulsed control circuitry enables an electro-mechanical servo system to control a resistive element interposed between the sacrificial anodes and the electrically bonded underwater parts. In an active mode of operation a current is applied directly to the anodes to quickly establish the proper level of correction which is maintained during the passive mode. Incremental corrections are made over a period of time to provide stabilization of the protection and to conserve power. A visual indication of the amount of protection is available at all times. Circuitry and indicating devices are included which facilitate location and correction of potentially harmful stray currents and to prevent loss of sacrificial anodes to nearby marine structures.
U.S. Pat. No. 4,544,465, which issued to March on Oct. 1, 1985, describes a galvanic anodes for submergible ferrous metal structures. The invention provides a detachable sacrificial anode unit comprising a rigid core, (e.g. a tubular steel member) and a body of sacrificial anode material (e.g. metals and alloys including zinc, aluminum and magnesium) surrounding and supported by the rigid core, wherein the ends of the rigid core extend beyond the ends of the body of sacrificial anode material and are adapted to be coupled to the end of another sacrificial anode unit to provide a rigid string. This invention also provides a submergible ferrous metal structure useful in a salt water environment and having a system to provide galvanic protection to the ferrous metal which system comprises a vertical oriented, rigid string of such sacrificial anode units secured to each other by threaded couplings and electrically connected to the ends thereof to such structure in a manner to provide galvanic protection to the structure.
U.S. Pat. No. 3,930,977, which issued to Wood on Jan. 6, 1976, describes a protection system for equipment and metallic fittings of non-metallic hulls of power boats. The system for protecting the personnel and the electrical equipment of power boats having non-metallic hulls and for the cathodic protection of the hulls of the metal fittings of such boats when docked and supplied from a shore-based alternating current supply, in which circuit breakers are inserted in the hot leg and the neutral leg of the shore-based alternating current supply is disclosed. It includes a polarity alarm and a polarity light socket in which is inserted a polarity light tester as described in U.S. Pat. No. 3,383,588, and in which the negative lead of the battery ground, the equipment ground, and the neutral leg of the shore-based alternating current supply are connected electrically with both the ground plate and the bonding ground of the boat.
U.S. Pat. No. 3,929,606, which issued to Wood on Dec. 30, 1975, describes a protection system for the metallic fittings non-metallic hulls of power boats. The system is intended for the cathodic protection of the metallic fittings of non-metallic hulls of power boats when such boats are docked and electrical power is supplied from a shore-based 110 volt alternating current supply. Novel circuitry, in which a battery charger is used to maintain all banks of storage batteries in operating condition, is combined with a flexible switching arrangement permitting the testing and charging of each bank of batteries, together or separately, and in which the negative leads of the battery charger, the banks of batteries, the equipment ground and the neutral leg of the shore-based alternating current supply are electrically connected with both the ground plate and the ship""s bonding ground of the boat to lessen or eliminate electrolysis.
U.S. Pat. No. 3,769,521, which issued to Caldwell et al on Oct. 30, 1973, describes an impressed current cathodic protection system. The system is intended for use with a marine structure and includes an elongated supporting member which can be lowered into position adjacent the underwater structure to be protected, an underwater power supply mounted in the supporting member for converting high voltage alternating current from a source above the water""s surface to low voltage direct current, one or more anodes mounted on the supporting member near the power supply, a potential controller for regulating the level of protection provided, and a reference cell for monitoring the system.
U.S. Pat. No. 3,636,409, which issued to Stephens, Jr. et al on Jan. 18, 1972, describes an electrical ground filter means for boats supplied with a shore-based source of alternating current power. An electrical ground filter means for boats or other vessels supplied with shore-based source of alternating current power has current leads and an electrical grounding lead connected between the alternating current source and a boat. The ground filter means comprises a first pair of rectifiers in series with each other, a second pair of rectifiers in series with each other and of opposite polarity with the first pair, a capacitor means, the first and second pairs of rectifiers and a capacitor means being connected electrically and parallel with each other.
U.S. Pat. No. 4,549,949, which issued to Guinn on Oct. 29, 1985, describes a marine propulsion device including cathodic protection. The marine propulsion device lower unit includes a housing having a lower portion submerged in water and defining an internal passage communicating with the water. Corrosion protection for both internal and external parts of the lower unit is provided with a sacrificial, galvanic type anode mounted on the submerged portion of the housing and including a first or outer portion having a surface exposed to water exterior to the lower unit and a second or inner portion having a surface exposed to water present in the passageway.
U.S. Pat. No. 5,011,583, which issued to Tanbara on Apr. 30, 1991, describes a corrosion prevention system for a marine propulsion system. A marine propulsion system of the type having a sacrificial anode for corrosion protection of the casing includes structure whereby the propeller is electrically insulated from the casing and the sacrificial anode. The structure includes spacers made of insulating materials, spacers having insulating coatings, or insulating coatings on the surfaces of the propeller or the propeller shaft. Electrical insulation of the propeller prevents unsightly and efficiency-reducing depositions on propeller surfaces and reduces the required size of the anode.
U.S. Pat. No. 3,953,742, which issued to Anderson et al on Apr. 27, 1976, discloses a cathodic protection monitoring apparatus for a marine propulsion device. A cathodic protection system monitor is coupled to an impressed current cathodic protection circuit used for corrosion protection of a submerged marine drive. The cathodic protection circuit includes one or more anodes and reference electrode mounted below the water line and connected to an automatic controller for supplying an anode current which is regulated in order to maintain a predetermined reference potential on the protected structure. A switch selectively connects a light emitting diode lamp or other light source between the controller output and ground so that the controller current may, when tested, be used to operate the light source in order to confirm that power is available to the anode.
U.S. Pat. No. 3,769,926, which issued to Race on Nov. 6, 1973, describes a marine galvanic control circuit. Apparatus is provided for minimizing galvanic deterioration of the metallic hull of a ship moored at a dock of a dissimilar metal, and receiving electrical power from a power source grounded to the dock, including a plurality of silicon diodes connected to an electrical power conductor is grounded at the dock and at the metallic hull of the ship. The intrinsic junction voltage drop of the diodes is sufficient to block current flow due to the voltaic cell effect between the ship""s hull and the dock.
U.S. Pat. No. 5,748,008, which issued to Landreth on May 5, 1998, describes an electrical integrity test system for boats. An electrical integrity test system for boats provides circuitry for evaluating the integrity of the boat""s electrical distribution AC grounding system when the boat is connected to a dock""s electrical distribution system, and the integrity of the boat""s galvanic isolator. The electrical integrity test system also includes a polarity detecting circuit that will activate an alarm when it detects a dock""s hot and neutral conductors to be reversed. Additionally, the electrical integrity test system includes an AC ground current detecting circuit that continuously monitors the boat""s AC grounding conductor for the presence of AC current. A system controller controls selected functions and sequence of functions of the described circuits. If the test system detects the AC grounding system or the boat""s galvanic isolator is faulty or the dock""s hot and neutral conductors are reversed or AC current flowing in the boat""s AC grounding conductor, it will activate an alarm to apprise the boat operator of the faulty condition.
U.S. Pat. No. 3,953,742, which issued to Anderson et al on Apr. 27, 1976, discloses a cathodic protection monitoring apparatus for a marine propulsion device. A cathodic protection system monitor is coupled to an impressed current cathodic protection circuit used for corrosion protection of a submerged marine drive. The cathodic protection circuit includes one or more anodes and a reference electrode mounted below the water line and connected to an automatic controller for supplying an anode current which is regulated in order to maintain a predetermined reference potential on the protected structure. A switch selectively connects a light emitting diode (LED) lamp or other light source between the controller output and ground so that the controller current may, when tested, be used to operate the light source in order to confirm that power is available to the anode.
U.S. Pat. No. 4,492,877, which issued to Staerzl on Jan. 8, 1985, discloses an electrode apparatus for cathodic protection. An electrode apparatus includes an insulating housing on which the anode and reference electrode are mounted and a copper shield mounted between the anode and electrode to allow them to be mounted in close proximity to each other. The shield is electrically connected to the device to be protected and serves to match the electrical field potential at the reference electrode to that of a point on the outboard drive unit remote from the housing.
U.S. Pat. No. 5,747,892, which issued to Staerzl on May 5, 1998, discloses a galvanic isolator fault monitor. A system and method for testing and monitoring the operation of a galvanic isolator is disclosed and illustrated. The galvanic isolator is positioned between the shore ground and boat ground to prevent the flow of destructive galvanic currents between the shore ground and the boat ground. The monitoring system transmits a test current through the galvanic isolator at specific time intervals to test the effectiveness of the galvanic isolator. The monitoring system includes a first counter that outputs an enabling signal after a desired period of time. The enabling signal allows a test current to flow through the galvanic isolator for a brief period of time. The enabling signal allows a test current to flow through the galvanic isolator for a brief period of time determined by a second counter. As the test current flows through the galvanic isolator, a current sensing circuit measures the test current and activates an alarm if the test current flowing through the galvanic isolator falls outside a predetermined range. In this manner, the monitoring system monitors and periodically tests a galvanic isolator.
U.S. Pat. No. 5,840,164, which issued to Staerzl on Nov. 24, 1998, discloses a galvanic isolator. The isolator protects against galvanic corrosion of a submersible metal marine drive. The galvanic isolator is positioned between shore ground and boat ground to prevent the flow of destructive galvanic currents between the shore ground and the boat ground while maintaining the safety function of a neutral ground. The galvanic isolator of the invention includes a blocking element positioned between the boat ground and the shore ground that can be switched between an open and a closed state by a trigger circuit. The trigger circuit closes the blocking element when the voltage difference between the boat ground and the shore ground exceeds a threshold value, such as 1.4 volts. During operation of the galvanic isolator during the high fault current situation, power is dissipated only the blocking element, rather than by the combination of the blocking element and trigger device. In this manner, the galvanic isolator reduces the amount of power dissipated during high current conditions and therefore reduces the amount of heat generated by the galvanic isolator.
U.S. Pat. No. 6,183,625, which issued to Staerzl on Feb. 6, 2001, discloses a marine galvanic protection monitor. A galvanic monitor system uses two annunciators, such like light emitting diodes, to alert a boat operator of the current status of the boat""s galvanic protection system. A reference electrode is used to monitor the voltage potential at a location in the water and near the component to be protected. The voltage potential of the electrode is compared to upper and lower limits to determine if the actual sensed voltage potential is above the lower limit and below the upper limit. The two annunciator lights are used to inform the operator if the protection is proper or if the component to be protected is either being over protected or under protected.
U.S. Pat. No. 5,032,095, which issued to Ferguson et al on Jul. 16, 1991, describes a marine engine with galvanic circuit protection which comprises an engine including a coolant jacket and an exhaust port, an exhaust gas discharge system including an exhaust gas manifold communicating with the exhaust port, a high-rise elbow communicating with the exhaust gas manifold, and an exhaust pipe communicating with the high-rise elbow and adapted to convey exhaust gas to an overboard discharge, a high-rise elbow and exhaust gas manifold coolant jacket surrounding the exhaust gas manifold and at least partially surrounding the high-rise elbow and communicating with the exhaust pipe for discharge of coolant from the high-rise elbow and exhaust gas manifold coolant jacket and through the exhaust pipe to an overhead discharge, which high-rise elbow and exhaust gas manifold coolant jacket includes a coolant discharge surface over which coolant is discharged from the high-rise elbow and exhaust gas manifold coolant jacket for flow to the exhaust pipe, a coolant conduit communicating between the engine coolant jacket and the high-rise elbow and exhaust gas manifold coolant jacket and including a portion extending at least as high as the discharge surface of the high-rise elbow and exhaust gas manifold coolant jacket and over which coolant flows, and a supply conduit for supplying coolant to the engine coolant jacket in response to engine operation.
U.S. Pat. No. 5,298,794, which issued to Kuragaki on Mar. 29, 1994, describes an electrical anticorrosion device for a marine propulsion device. The device primarily relates to an electrical anticorrosion device for a marine propulsion arrangement. More particularly, the invention relates to a cathodic protection arrangement which is suitable for use with an inboard/outboard propulsion unit. According to the invention, an anode and a reference electrode are housed with a housing unit which is mounted upon a propulsion unit mounting bracket. The two electrodes are arranged so that each is essentially equidistant from a point located approximately midway across the lateral width of an outboard drive unit, which unit is secured to the mounting bracket when the unit is positioned for driving the associated watercraft in a generally forward direction. The electrode housing further serves as a low speed/idle exhaust gas device which breaks up exhaust gas bubbles which otherwise might cause loud and objectionable noise. Thus, the invention allows for the effective prevention of cathodic corrosion by insuring that a proper current is supplied to a sacrificial anode and, additionally, allows for improved silencing for the low speed/idling exhaust gases of an inboard/outboard drive unit.
The patents described above are hereby expressly incorporated by reference in the description of the corrosion inhibiting system of the present invention.
As is well known to those skilled in the art, various types of control circuits can be operated either as an open loop system or a closed loop system. In an open loop system, a preselected output, such as a current level, is provided and the resulting effect of that output, such as a changed voltage level, is not used to change the output magnitude. In certain applications, empirical information can be used to predetermine the magnitude of the output with the assumption that the resulting effect can be predicted without actually being measured dynamically. In a closed loop system, the effect (e.g. voltage level) of the output (e.g. current level) is measured and used to change the magnitude of the output in order to control the resulting effect within a preselected range. It would be beneficial if a corrosion inhibiting system, such as a cathodic protection circuit or galvanic corrosion protection circuit, could be provided in which the circuitry is able to adapt to either an open loop system or a closed loop system.
The adaptive capability of such a circuit has two significant advantages. One advantage is that the failure of a monitoring device, such as the electrode 500 which is described in greater detail below, does not disable the operability of the system. In other words, if the electrode 500 fails for any reason and an appropriate signal is not obtained from the electrode, the circuit can operate in a manner which does not require a signal input from the electrode. In other words, the circuit can adapt by reverting to an open loop control process. If, on the other hand, an appropriate signal is available from the electrode 500, the circuit can operate as a closed loop system. A second advantage of an adaptive control system is that one circuit can be used in conjunction with the system, regardless if the system is intended for use with an electrode or without. In other words, two types of system can be provided and sold with the only difference between the two types of system being the inclusion or exclusion of an electrode connected to the control circuit.
A method for inhibiting corrosion of a component of a marine vessel when the electrical system of the marine vessel is connected in electrical communication with an electrical conductor, in accordance with the preferred embodiment of the present invention, comprises the steps of providing a first circuit point which is connectable in electrical communication with a component and a second circuit point which is connectable in electrical communication with the electrical conductor. It also comprises the step of monitoring a voltage potential of a third point which is representative of the voltage potential proximate the first point. It should be understood that, in the terms used to describe the present invention, the term xe2x80x9cmonitoringxe2x80x9d can either include the step of measuring a voltage with an electrode or recognizing that the signal from an electrode is absent, whether or not an electrode is connected or not. In other words, if a system is configured without any electrode provided to measure the voltage potential at the third point, described above, monitoring the voltage potential will provide sufficient information to determine that the electrode is not included in the circuit and the actual measuring of the voltage potential is not necessary.
The present invention further comprises the step of causing an electronic current to flow in a direction from the second point to the first point, wherein the electric current is controlled according to a first process or a second process. It is controlled according to the first process when the voltage potential of the third point is above a preselected threshold magnitude. The electronic current is controlled according to the second process when the voltage potential of the third point is below the preselected threshold magnitude. In other words, if the monitoring of the voltage potential of a third point (e.g. the electrode 500) is below a preselected threshold magnitude, the present invention presumes that the electrode is either not included in the system or, if included, is not functioning normally. In either case, the present invention can adapt by controlling the electric current according to the second process.
The first process comprises the step of selecting an imposed magnitude of electronic current as a function of the voltage potential of the third point in order to achieve a predetermined target-magnitude of the voltage potential at the third point. In other words, the first process is a closed loop process in which the electronic current magnitude is changed as a function of the measured voltage at the third point, by the electrode 500. The second process comprises the step of selecting an imposed magnitude of electric current independently of the voltage potential of the third point. In other words, if the electrode 500 is either missing from the system or not operable to provide a voltage signal above the preselected threshold, the present invention adapts to this missing electrode by reverting to an open loop process by using a preselected fixed imposed current level.
The causing step is performed periodically and is followed by periods of time when no electronic current flows in a direction from the second point to the first point in a particularly preferred embodiment. In other words, the electronic current is pulsed. The voltage potential of the third point is measured relative to the voltage potential of the first point in a preferred embodiment of the present invention. In certain embodiments, the third point can be located on a transom of a marine vessel on which the marine propulsion device is supported. The third point is preferably located within 12 inches of the marine propulsion device. The first and second circuit points are connectable, to a ground wire of a three wire electrical power cable which is connected in electrical communication between a shore-based source of electrical power and an electrical system of a marine vessel. The predetermined target magnitude of the voltage potential of the third point is generally equal to 0.94 volts in a preferred embodiment of the present invention and the preselected threshold magnitude is approximately 0.10 volts.